Currently there are two common ways to manufacture rubber vibration isolators. Each involves a steel tube or inner metal link bushing surrounded by vulcanized rubber. The steel tube gives the isolator rigidity and provides the means to attach the device. The first method, method A, utilizes a preformed and cured rubber piece. The metal link bushing is coated with a rubber adhesive and pressed into the rubber piece. The adhesion sometimes breaks down and tends to separate the bushing from the rubber. The second and preferred method of manufacturing, method B, places the adhesive coated metal link bushing inside of a mold. The rubber is injected under pressure into the mold and the vibration isolator is cured as one unit. The benefit of this technology, method B, is the bond between the bushing and the rubber is much stronger than under method A. Under method B, the rubber will typically tear before the adhesive gives way.
Each of these methods uses a different raw product for the bushing. Method A uses a flat steel stock which, as described below, is progressively formed into a tube. Heretofore, method B has used “drawn over mandrel” (DOM) tubing or welded seam tubing. The raw material cost for DOM tubing is roughly 3–4 times that of flat stock used in forming tubing. The main reason for not heretofore using tubing formed from flat stock for method B, under which rubber is injection molded around tubing positioned in a mold, is seepage of rubber through the seam of the tubing due to the high pressure. Removing this material after curing is troublesome and not cost effective.